Conventionally, various methods have been performed to reduce multiple-reflection echoes in an ultrasound image (B-mode image) that hinder diagnosis. As one example of such methods, a method is known of compounding, by averaging, a plurality of B-mode images at different deflection angles of ultrasound transmission and reception. A method is also known in which this method is applied for estimating the levels and the positions of multiple-reflection echo components from the B-mode images at different deflection angles to adaptively control weights for the averaging based on the estimation result.
Due to the limitation of the element factor, however, the above-described methods of compounding a plurality of images at different deflection angles are inevitably subject to the influence of amplitude reduction in elements at aperture edges, which becomes noticeable when the deflection angles are increased. Specifically, the lateral resolution of an obliquely tilted image is low due to its smaller effective aperture in comparison with an image (central image) at a regular deflection angle of “0°”. Furthermore, in the obliquely tilted image, the sensitivity (S/N ratio) is also low compared with the central image. Thus, in an output image compounded with a plurality of images at different deflection angles, the lateral resolution and the sensitivity are lower than those of a regular central image.